1. Field of the Invention
The present invention relates to a flat panel for displaying an image, and more particularly, to a liquid crystal panel. Also, the present invention relates to a liquid crystal display device (LCD) having a liquid crystal panel and a driving method thereof.
2. Description of the Related Art
Related Art flat panels such as a liquid crystal panel, a plasma display panel, a light emitting display panel and so on are advantageous because of their lightweight and slim profile. These flat panels are and they are replacing cathode ray tubes (CRTs). In the liquid crystal panel, an electric field varying with pixel data of video signals is applied to each pixel. Due to the applied electric field, light transmittance of liquid crystal cells is adjusted and then images are displayed.
Liquid crystal cells included respectively in the liquid crystal panel are commonly connected to a common voltage line. Therefore, the respective liquid crystal cells are charged with pixel voltage signals varying with respect to a common voltage. In other words, the pixel voltage signal supplied to the liquid crystal cell has a difference voltage from the common voltage. Thus, the related art liquid crystal panel dissipates a large amount of driving power.
Also, the related art liquid crystal panel is driven in an inversion system so as to improve a response characteristic of liquid crystal with respect to the pixel voltage signal. The inversion driving system includes a frame inversion system, a line (or column) inversion system, and a dot inversion system. The frame inversion system inverts the polarity of the pixel voltage signal according to the change of frames, and the line (or column) inversion system inverts the polarity of the pixel voltage signal according to the change of lines. The dot inversion system inverts the polarity of the pixel voltage signal according to the change of pixels. According to these inversion driving systems, positive pixel voltage signals and negative voltage signals may be applied to the liquid crystal panel at the same time. Here, the positive pixel voltage signals represent signals that vary in a positive polarity (+) region with respect to the common voltage, and the negative pixel voltage signals represent signals that vary in a negative polarity (−) region with respect to the common voltage. Hence, a swing width of the pixel voltage signal applied to the liquid crystal panel increases. Consequently, in the case of the liquid crystal panel driven by the inversion driving system, impulse type noises are generated and the driving power consumption increases.
These problems will be described in more detail with reference to FIG. 1. FIG. 1 is a schematic view of a related art LCD. In FIG. 1, the related art LCD includes a liquid crystal panel 2 connected to a gate driver 4 and a data driver 6. The liquid crystal panel 2 has a plurality of pixels PXL at regions defined by crossings of a plurality of data lines DL1 to DLm and a plurality of gate lines GL1 to GLn. Each of the pixels includes a liquid crystal cell CLC and a thin film transistor (TFT). The liquid crystal cell CLC is connected to a common voltage line Vcom extending from a common voltage generator 9, and the TFT switches a pixel voltage signal supplied from a corresponding data line DL to the liquid crystal cell CLC in response to a scan signal of a corresponding gate line GL. Because the liquid crystal cell CLC of the pixel PXL is connected to the common voltage line Vcom, the pixel voltage signal supplied to the liquid crystal cell CLC has a difference voltage from the common voltage Vcom. Hence, the pixel voltage charged at each liquid crystal cell and the swing width of the pixel voltage signal output to each data line DL increases. Consequently, the related art liquid crystal panel has high driving power consumption.
In addition, the pixels PXL of the liquid crystal panel 2 can be driven by the inversion system. For example, as illustrated in FIGS. 2A and 2B, each of the pixels can be driven by a pixel voltage signal in which the polarity is inverted for each frame. Also, the polarity is inverted with respect to the pixel voltage supplied to adjacent pixels. FIG. 2A illustrates polarity patterns of the pixel voltage signal supplied to each pixel of the liquid crystal panel 2 when images of odd (or even) frames are displayed, and FIG. 2B illustrates polarity patterns of the pixel voltage signal supplied to each pixel of the liquid crystal panel 2 when images of even (or odd) frames are displayed. To supply the polarity-inverted pixel voltage signals to the adjacent pixels at each frame, the data driver 6 converts pixel data from the timing controller 8 into analog pixel voltage signals and inverts the polarity of the converted pixel voltage signals at each frame and horizontal sync period according to the data lines DL1 to DLm. Therefore, if the pixel voltage signal supplied to the data lines DL1 to DLn has a positive voltage during one frame or one horizontal sync period as illustrated in FIG. 3, it has a negative voltage during a next frame or next horizontal sync period.
As described above, if the liquid crystal panel is driven by the inversion system, the pixel voltage signal alternately has a positive voltage and a negative voltage with respect to the common voltage and the swing width also increases. Consequently, the related art liquid crystal panel and the LCD having the same have problems of driving power consumption increases and the occurrence of impulse type noise.